1. Field of the Invention
The present invention relates to a method for sulfonating olefins. More specifically, it relates to a method for sulfonating olefins in which the sulfonation efficiency of internal olefins is improved.
2. Description of the Prior Art
Internal olefin sulfonates are known as surfactants having excellent penetrating power and low temperature stability. However, they have not been generally used due to production problems. That is, alpha-olefins having structures similar to those of internal olefins have a high reactivity to sulfur trioxide SO.sub.3 and readily form alpha-olefin sulfonates. However, although a sulfonation efficiency of internal, olefins having 8 to 14 carbon atoms is up to approximately 94% by weight, the reactivity, to SO.sub.3, of internal olefins having more than 15 carbon atoms is remarkably decreased and the conversion is at most approximately 89%, even when various attempts to increase the reactivity, for example, the increase in the SO.sub.3 mol ratio are made For this reason, a large amount of unreacted oil (i.e., olefins) remains in the sulfonated products, which cannot be directly utilized in various application fields such as detergent compositions.
Various attempts have been made to solve these problems. For example, U.S. Pat. No. 4,183,867 proposes a two-step sulfonation method in which the unreacted oil is further reacted by adding sodium sulfonate thereto, followed by the addition of sulfuric acid to effect the sulfonation. Japanese Unexamined Patent Publication (Kokai) No. 54-14918 proposes extraction of the unreacted oil with a solvent, to recover the unreacted oil. U.S. Pat. No. 3,893,940 proposes recovery of the unreacted oil by stripping. However, the above-mentioned two-step sulfonation method in which sodium sulfate is added is disadvantageous in that the resultant products are limited in their utility fields due to the increase in the inorganic contents. The above-mentioned methods for separating the unreacted oil by solvent extraction or stripping are not preferable from the economical point of view since the separation and recovery steps of the unreacted oil are complicated. Furthermore, the use of solvents causes difficulty in the complete removal of the solvents from the resultant products, and increases costs due to the use of the solvents.